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Quantitative analysis of NaI(Tl) gamma-ray spectrometry using an artificial neural network
Kim, Jinhwan,Lim, Kyung Taek,Kim, Junhyeok,Kim, Chang-jong,Jeon, Byoungil,Park, Kyeongjin,Kim, Giyoon,Kim, Hojik,Cho, Gyuseong Elsevier BV * North-Holland 2019 Nuclear Instruments & Methods in Physics Research. Vol. No.
<P><B>Abstract</B></P> <P>In this manuscript, we propose an algorithm based on an artificial neural network (ANN) for the analysis of the NaI(Tl) gamma-ray spectra with radioisotope (RI) mixtures to identify RIs and determine the relative activity levels of the identified RIs. The ANN was trained based on the spectra that were generated by synthesizing previously identified spectra from single RIs, considering the characteristics of the measurement environments, such as gain shift effects and statistical fluctuations in the spectrum. The proposed ANN was evaluated through several measured spectra that contained up to six certified reference materials for a quantitative analysis. We also evaluated the shift in the spectra due to temperature variations in the range of 0–50 °C and the low-count spectra with a one-second acquisition period. These results were compared with those from an ANN trained through simulated spectra to emphasize the importance of acquiring a high-quality training dataset. In addition, we show that complex low-resolution spectra can be accurately analyzed with the proposed ANN under various scenarios, in which the maximum root mean square error was found to be 2.8%.</P>
(Na, K)NbO3-Based Ceramics for Self-Powered Energy Harvesting Applications.
Kim, Jinhwan,Koh, Jung-Hyuk American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.3
<P>Self-powered energy harvesting technologies have been intensively investigated by employ- ing Pb-free piezoelectric materials. One such Pb-free piezoelectric material, the ceramic 0.97(Na0.5K0.5)NbO3-0.03(Bi0.5Na0.5)TiO3, was prepared by employing the conventional mixed oxide method. 0.97(Na0.5K0.5)NbO3-0.03(Bi0.5Na0.5)TiO3 ceramics were prepared and the effect of sintering temperature on the microstructure, piezoelectric and ferroelectric properties were system- atically investigated for energy harvesting applications. The crystal structure of 0.97(Na0.5K0.5)NbO3- 0.03(Bi0.5Na0.5) TiO3 Pb-free piezoelectric ceramics, sintered at temperatures between 1080 °C and 1160 °C, was examined by X-ray diffraction analysis. The dielectric properties of 0.97(Na0.5K0.5)NbO3-0.03(Bi0.5Na0.5)TiO3 ceramics were measured from 1 kHz to 1 MHz for the various sintering temperatures. We expect that optimization of sintering parameters can improve the piezoelectric and ferroelectric properties of 0.97 (Na0.5K0.5)NbO3-0.03(Bi0.5Na0.5)TiO3 ceramics for energy harvesting.</P>
Laser Etching Effects for Ag Electrodes on Flexible Indium Tin Oxide Thin Films
Kim, Jinhwan,Ji, Jae-Hoon,Lee, Hyeongjae,Min, Sung-Wook,Kim, Sung-Jin,Chang, Seung Wook,Koh, Jung-Hyuk American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.12
<P>A nano-second infrared (IR) laser with a wavelength of 1064 nm was employed to investigate the etching properties of Ag paste on flexible indium tin oxide (ITO)/PET thin films. The IR laser was employed to obtain the feasibility and effectiveness of etching Ag paste. Different types of IR laser can be used for aligning, evaporation, and the etching process depending on their wavelength and power. Because a laser has a coherent single wavelength with high power, it can be used for the etching process. Further, the power and position of any type of laser can be accurately controlled during the process. Even uniformly deposited Ag paste can be accurately removed without touching and affecting another layer on the flexible substrate. Spin-coated Ag paste on flexible ITO thin films can be etched accurately. We believe that 1064 nm IR laser can be the best tool for etching process applications in semiconductor technologies.</P>
Kim, Jinhwan,Kim, Kyungmin,Lee, Jaiyong IEEE 2017 IEEE Transactions on Vehicular Technology VT Vol.66 No.1
<P>Cooperative hybrid automatic retransmission request (C-HARQ) is a simple and effective method for wireless communication. Since its performance largely depends on the selection of a relevant relay, the design of an appropriate relay selection scheme is very important. Although various works have been performed on this topic, most of them did not take into account both the “<B><I>not memoryless</I></B>” and multiple retransmission characteristics of C-HARQ, resulting in the loss of achievable performance. In this paper, we propose a novel cooperative relay selection scheme in a distributed manner called transmission number relaying (TNR) to simultaneously reduce the outage probability and increase the energy efficiency by utilizing the features of C-HARQ. The TNR scheme determines a single relay based on the estimated number of transmissions, which is calculated from the channel condition. Using these numbers instead of just the channel condition improves the outage probability and reduces the total consumed energy. The exact probability of the number of transmissions at each relay and the outage probability are analyzed, and the numerical results show that the proposed scheme significantly improves the outage probability and reduces the total consumed energy. In addition, when the number of available relays is small, the proposed scheme achieves high energy efficiency.</P>
Antiferromagnetic coupling of van der Waals ferromagnetic Fe<sub>3</sub>GeTe<sub>2</sub>
Kim, Dongseuk,Park, Sijin,Lee, Jinhwan,Yoon, Jungbum,Joo, Sungjung,Kim, Taeyueb,Min, Kil-joon,Park, Seung-Young,Kim, Changsoo,Moon, Kyoung-Woong,Lee, Changgu,Hong, Jisang,Hwang, Chanyong IOP Pub 2019 Nanotechnology Vol.30 No.24
<P>Among two-dimensional (2D) layered van der Waals materials, ferromagnetic 2D materials can be useful for compact low-power spintronic applications. One promising candidate material is Fe<SUB>3</SUB>GeTe<SUB>2</SUB> (FGT), which has a strong perpendicular magnetic anisotropy and relatively high Curie temperature. In this study, we confirmed that an oxide layer (O-FGT) naturally forms on top of exfoliated FGT and that an antiferromagnetic coupling (AFC) exists between FGT and O-FGT layers. From a first-principles calculation, oxide formation at the interface of each layer induces an AFC between the layers. An AFC causes a tailed hysteresis loop, where two-magnetization reversal curves are included, and a negative remanence magnetization at a certain temperature range.</P>
Kim, Jinhwan,Park, Kyeongjin,Cho, Gyuseong Elsevier 2019 Applied radiation and isotopes Vol.147 No.-
<P><B>Abstract</B></P> <P>Radioisotope identification using a plastic scintillation detector has been a challenging issue because of the poor spectral resolution and low cross-sections of these types of detectors when used for photoelectric absorption. In this paper, we propose an algorithm that identifies a single radioisotope and multiple radioisotopes from the gamma spectrum of a plastic scintillator using an artificial neural network. The spectra were simulated using Monte Carlo N-Particle Transport Code 6 to formulate the training set, and the spectra were measured by a two-inch EJ-200 to create the test set (1440 spectra in total). The ANN-based algorithm presented here ensures an identification accuracy of 98.9% for a single radioisotope and 99.1% for multiple radioisotopes. Even if the spectra were intentionally shifted by 36 keV for low and high energies, the trained ANN predicts radioisotopes with high accuracy. In addition, we have determined the minimal required number of detected counts to identify the radioisotope with 5% false negative and false positive.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Multi-radioisotopes were identified using an artificial neural network (ANN). </LI> <LI> The ANN was trained with simulated spectra by MCNP6. </LI> <LI> The algorithm was evaluated using measured plastic gamma spectra. </LI> <LI> Shifted spectra were also evaluated by the trained ANN. </LI> </UL> </P>
Microfluidic Fabrication of Multistimuli-Responsive Tubular Hydrogels for Cellular Scaffolds
Kim, Dongwan,Jo, Ara,Imani, Kusuma Betha Cahaya,Kim, Dowan,Chung, Jin-Woong,Yoon, Jinhwan American Chemical Society 2018 Langmuir Vol.34 No.14
<P>Stimuli-responsive hydrogel microfibers and microtubes are in great demand for biomedical applications due to their similarity to the native extracellular matrix. In this study, we prepared pH- and temperature-responsive hydrogel microfibers and microtubes using a microfluidic device through alginate-templated photopolymerization. Hydrogel monomer solutions containing <I>N</I>-isopropylacrylamide (NIPAm) and sodium acrylate (SA) or allyl amine (AA) were irradiated with UV light to invoke in situ photopolymerization. A repulsive force between the ionized SA or AA groups caused by protonation/deprotonation of the acrylate or amine groups, respectively, led to changes in the diameters and wall thicknesses of the fibers and/or tubes depending on the pH of the medium. Poly(NIPAm) is a well-known thermally responsive polymer wherein the NIPAm-based copolymer microfibers exhibited a thermal behavior close to the lower critical solution temperature. We have demonstrated that these multistimuli-responsive volume changes are fully reversible and repeatable. Furthermore, the positively charged microfibers were shown to exhibit cell adhesion, and the number of cells attached to the microfibers could be further increased by supplying nutrients, presenting the possibility of their application in tissue engineering and other biomedical fields.</P> [FIG OMISSION]</BR>